JP2880175B2 - Laser annealing method and thin film semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser annealing method in manufacturing a thin film semiconductor device, and more particularly to a laser annealing method suitable for an active matrix type display.

[Conventional technology]

Recently, a thin film transistor (Thin Film Transistor, abbreviated as TF)
T) As a material, polycrystalline silicon (Polycrystalline Silicon, abbreviated as poly-Si), which is excellent in terms of high image quality, is used. This Poly-Si film is formed by a low pressure CVD method (LPCVD
Method and the normal pressure CVD method (APCVD method).
Quartz glass or a normal glass plate is used as the insulating substrate. When a normal glass plate is used, the maximum temperature is about 640 ° C, so there is a big restriction.Therefore, there is a method to recrystallize by irradiating only the surface layer of the poly-Si film with laser without thermally affecting the glass plate. Attempted. According to this method, the crystallinity is improved as compared with low-temperature thermal annealing that does not affect the glass plate.

Conventionally, as this laser irradiation method, a method for manufacturing a semiconductor device by irradiating an ultraviolet light pulse laser having a large absorptivity with a Si film as described in JP-A-60-245124 has been studied.

[Problems to be solved by the invention]

In the above prior art, the TFT characteristics were improved by improving the crystallinity by laser irradiation.
The crystal orientation of the y-Si film has not been studied
There is a possibility of further improving the carrier mobility when creating the.

An object of the present invention is to obtain a larger carrier mobility by considering the structure of a thin film semiconductor device for improving the characteristics of the thin film semiconductor device, particularly the orientation of a Poly-Si film used for an active layer of a TFT. It is in.

[Means for solving the problem]

The above object is achieved by providing a poly-Si layer constituting a TFT, which is a semiconductor device formed on an insulating substrate such as a glass substrate, to have an orientation mainly composed of {111} planes.

This Poly-Si layer is deposited at a substrate temperature of 550 ° C. or less by a reduced pressure CVD method with a thickness of 1500 ° or less, and a Si film deposited at 500 ° C. or less is 200 mJ / cm ² or more, and Si deposited at 520 to 550 ° C. The film emits laser light with a light intensity of 400 mJ / cm ² or more.
-Obtained by irradiation from the Si layer side. When the thickness of the Si film deposited at 550 ° C is reduced,
MJ / cm ² or more, the film thickness of 600~800Å 300mJ / cm ² or more, 6
When the film thickness is not more than 00 °, it can be obtained by irradiating laser light from the Poly-Si layer side with a light intensity of 200 mJ / cm ² or more.

[Action]

Poly-Si layers recrystallized by laser irradiation
There are few defects in the Si crystal and the trap of electrons is greatly affected by the grain boundaries. The interface charge density at the grain boundaries of Poly-Si is
The interface charge density between each crystal plane of Si single crystal and SiO ₂ is <100
>, <110>, and <111>, the same relationship holds, and the {111} dominant orientation of the Poly-Si film is more perpendicular to the film than that of the Poly-Si film, in which no orientation is observed. The trap density in the (<111> direction) increases. On the other hand, in the direction parallel to the film, the poly-Si film with {111} dominant orientation has no orientation.
The trap density is relatively lower than that of the oly-Si film. If the trap density is low, the width of the depletion layer generated at the grain boundary becomes narrow, and the potential barrier here becomes low. Po
The carrier mobility of ly-Si is mainly determined by the height of the potential obstacle at the grain boundary. TET's carrier is Poly-Si
Flows parallel to the membrane. From these conditions, the mobility of the carrier is relatively large in Poly-Si having {111} dominant orientation as compared with Poly-Si having no orientation.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

FIG. 1 shows a sectional structure of the whole TFT using the present invention.
The substrate 1 is a glass substrate having a strain temperature of about 640 ° C. Substrate 1 to 5
An LPCVD film is deposited at a pressure of 1 Torr using a monosilane gas diluted to 20% with helium at a temperature of 50 ° C.
The deposition time is 85 minutes, and a 1500Å film is deposited. Next, the substrate 1 is kept at 480 ° C., and a surface protection film is deposited at 1000 ° C. for about 8 minutes by atmospheric pressure CVD using monosilane gas diluted to 4% with helium and oxygen as raw materials. The LPCVD film was recrystallized by irradiating an ultraviolet pulse laser (wavelength: 308 nm, pulse width: 25 ns) using XeCl as a gas source from the upper surface of this film to recrystallize the Poly-S
The i-films 2, 3, and 4 are obtained. At this time, by setting the laser light intensity to 400 mJ / cm ² or more, the main orientation of the Poly-Si film becomes {111} dominant orientation, and the average crystal grain size is about 1000 °. Next, the SiO ₂ film used as the surface protective film is removed with a hydrofluoric acid aqueous solution. After passing through a photo-etching step of forming a Poly-Si film recrystallized by laser irradiation into an island shape, an SiO ₂ film 5 for a gate insulating film is deposited by a normal pressure CVD method. Next, a Poly-Si film 6 for a gate electrode is deposited at 550 ° C. and 1 Toor for 3500 °. After the gate film 5 is photo-etched, the source and drain regions 3 and 4 are implanted. The conditions are phosphorus (P), a dose of 5 × 10 ¹⁵ cm ⁻² and a voltage of 30 KeV.
A passivation film 8 made of phosphor glass is deposited at 480 ° C. for 500
The implant region is activated by heat treatment in N ₂ at 600 ° C. for 20 hours or more, or irradiation with an ultraviolet pulse laser at a light intensity of 200 mJ / cm ² or more in N ₂ . After the photo and etching process for contact, the Al electrode 7
TFT is formed by 6000Å spatter.

Fig. 2 shows the substrate temperature of Poly-Si reduced to 550 ° C by low pressure CVD.
1500Å, and the light intensity from the Poly-Si side is 100
The X-ray diffraction intensity from each surface and the change in the mobility of the TFT formed by the above method when re-assembled by irradiating an ultraviolet pulsed laser while changing the thickness between -400 mJ / cm ² are shown. The Si (111) diffraction peak with the highest diffraction intensity has a threshold energy (about 100
Above mJ / cm ² ), it increases in proportion to the light intensity, but other Si
The (220) and Si (311) diffraction peaks decrease in increasing amount at a light intensity of 300 mJ / cm ² or more, and the orientation becomes {111} dominant orientation. ｛111｝
At a light intensity of 300 mJ / cm ² or more, which is the dominant orientation, the mobility increases sharply.

Next, as shown in FIG. 3, an LPCVD film is deposited at a deposition temperature of 500 to 600 ° C. when depositing by the low pressure CVD method, and then a surface protective film is deposited in the same manner as described above. 3 shows the crystal orientation of the obtained Poly-Si film. The LPCVD film deposited at a substrate temperature of 500 ° C. 200 mJ / cm ² or more, 520 to
Irradiation with laser light with a light intensity of 400 mJ / cm ² or more in a Si film deposited at 550 ° C resulted in a {111} dominant orientation, while a Si film deposited at a substrate temperature of 580 ° C or more showed a {111} dominant orientation. Absent.

Next, as shown in FIG. 4, the deposition temperature was reduced to 550 ° C. and the deposition time was reduced to 400 to 1500
After depositing with a film thickness of Å, a surface protective film was deposited in the same manner as described above, and then irradiated with an ultraviolet pulse laser to recrystallize Po.
4 shows the crystal orientation of a ly-Si film. 400mJ / cm for 1500mm thickness
In ^more 800 Å 300 mJ / cm ² or more, the 600Å and 400 Å 200
Irradiation with laser light at a light intensity of mJ / cm ² or more
1｝ Dominant orientation.

The Poly-Si film having a main orientation of {111} described in this embodiment has a high mobility, and excellent electrical characteristics can be obtained by using this in the active region of the TFT.

〔The invention's effect〕

According to the present invention, even if the deposition conditions of the LPCVD film are different, a poly-Si film having a {111} dominant orientation can be obtained by optimizing the light intensity of the irradiation ultraviolet light pulsed laser beam. A large thin film semiconductor device can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the structure of the TFT of the present invention, FIG. 2 is a diagram showing the light intensity dependence of the crystallinity and mobility of Poly-Si after laser annealing, and FIGS. 3 and 4 are Poly-Si. FIG. 3 is a view showing the crystal orientation of a Si film. DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Polycrystalline silicon layer, 3 ... Source region, 4 ... Drain region, 5 ... Gate insulating film, 6 ... Gate electrode, 7 ... Al electrode, 8 ... Passivation film.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshiaki Okajima 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi Ltd. (56) References JP-A-61-127118 (JP, A) 32527 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/20

Claims (4)

(57) [Claims] 1. A polycrystalline silicon film having a thickness of 1500 ° or less,
500 ° C. The polycrystalline silicon film deposited below 200 mJ / cm ² or more, 400 meters in a polycrystalline silicon film deposited at 520 ° C. to 550 ° C.
A laser annealing method characterized by irradiating a laser beam having a light intensity of J / cm ² or more from the polycrystalline silicon film side to impart an orientation mainly including a {111} plane. 2. A polycrystalline silicon film having a thickness of 1500 ° or less,
500 ° C. The polycrystalline silicon film deposited below 200 mJ / cm ² or more, 400 meters in a polycrystalline silicon film deposited at 520 ° C. to 550 ° C.
A thin-film semiconductor device characterized in that a laser beam having a light intensity of J / cm ² or more is irradiated from the polycrystalline silicon film side so that the {111} plane is mainly oriented. 3. An Si film deposited at a temperature of 550.degree.
400 mJ / cm ² or more for Å film thickness, 3 for 600Å-800 膜厚 film thickness
For a film thickness of not less than 00 mJ / cm ^{2 and not} more than 600 °, laser light having a light intensity of not less than 200 mJ / cm ² is irradiated from the Si film side to obtain {111}.
A laser annealing method characterized by giving an orientation mainly to a surface. 4. An Si film deposited at a temperature of 550 ° C. or less, from 800 ° to 1500 ° C.
400 mJ / cm ² or more for Å film thickness, 3 for 600Å-800 膜厚 film thickness
For a film thickness of not less than 00 mJ / cm ^{2 and not} more than 600 °, laser light having a light intensity of not less than 200 mJ / cm ² is irradiated from the Si film side to obtain {111}.
A thin-film semiconductor device characterized by having an orientation mainly based on a plane.